OPTIMALLARGE SCALE WATER TRANSFERS IN SPACE AND TIME

Abstract

In the domain of planning for optimal development, supply management is a crucial issue. Given the uncertainties and vagaries associated with monsoon precipitation in space and time, and given the ever increasing demands from consumptive and nonconsumptive uses of water, the mismatch between the supply and demands is increasing day by day. From the perspective of supply management, inter basin transfer has been considered as one of the options. While planning for transfer of water, it becomes imperative to know beforehand the expected behaviour on the water availability at export points planned for above. Systemsanalysis provides the answer as an approach to estimate the yield at the export point. Inter-basin transfer of water is a gigantic exercise encompassing wide spectrum of fields and is highly complex. The evaluation of such an exercise can best be accomplished with the help of systems analysis. There are a number of techniques employed in systems analysis. By far, the most important of all is optimization by linear programming where the objective function and constraints are linear functions of decision variables. Among different L.P. models, Reservoir Yield Model has many distinct advantages. It has the advantage of dealing with very large size of problem efficiently. As compared to the complete model, there is a substantial reduction in the problem size with reasonable estimates of over-year and within-year reservoir capacity requirements. Further the model has advantages of taking into account the critical year flows and allowable deficit in a dry year. The available yield model has been modified to take into account the transfer criteria from different states, basinsand reservoir and is coined as the Generalised Reservoir yield Model (GRYM). The model takes into account the transfer from a point to another by has the capability to analyse at the level state (province in India), basin level and reservoir level. The improved model, GRYM is applied to the study area, which comprises the first part of the peninsular component of the National Perspective Plan, 1980 of Government of India. The area almost covers the entire basins of major peninsular rivers of India, namely, the Mahanadi, the Godavari, the Krishna, the Pennar and the Cauvery. The combined area of thesebasin is in excess of 8 lakh sq. km and covers more than 25% of the area of India. There are about 200 major, 900 medium and a large number of minor ii irrigation projects. Due to the large size of the problem, only major reservoir projects have been considered in the study. The contributions of the medium and minor irrigation projects have been lumped together for their contributions to the inflow, utilisations and demand scenario. For the inflow data, the period chosen for analysis is 28 years i.e., from 1972-73 to 1999-2000. Within year analysis has been made for 12 within-year time periods for the critical year.The water year in India starts in the month of Juneand ends in May. Annual reliabilities for the firm and secondary yields considered are 97 percent and 76 percent based on weibull plotting position for a data series of 28 years, respectively. The net inflow series at each project are calculated by the basin water balance method from the discharge data available at nearby river gauging site. In order to process voluminous data available and received from different organisations in different formats and to place them on uniform platform, different FORTRAN programs are written and utilised. Failure years at each project are identified from the respective net inflow series. The inflow fractions in within-year time periods are calculated for each reservoir considering inflow of the driest year. Storage area curves (linearized over dead storage) are used for computation of evaporation parameters. Demands from different sectors have been considered for a time horizon of 2050 AD. The reason for adopting the planning horizon is due to the fact that the population in India is expected to stabilise in 2050 AD and consequently the demand patterns will also be realistic. The gross irrigation water requirements at each within-year time period of the proposed crop plan under each project is estimated by using FAO-56. Population of the basin in year 2001 is calculated from the district census data and then projected for year 2050. Population of a sub-basin is distributed proportionately among all the projects in proportion of their respective culturable/cultivable command area (CCA). Municipal and industrial water demand at each project is calculated for projected populationx Sitespecific values of allowable percentage yield (failure fraction) for satisfying the project specific demands as far as possible in successful years have been considered in the study. Protein and calorie requirements of the total as well as of the agricultural population have been computed. After the flow parameters or the supply parameters, demand parameters and the parameters pertaining to the physical parameters are known, they are put to the model. In order to write the large number of equations into the solver, again FORTRAN programmes are used. The matrix so generated is solved by using LINDO iii software.Thestudy is limited to the surface water resources and also for major projects only. The model was successfully applied on the study area comprising of five major river basins of peninsular India. The outcomes of the results have been analysed and put in Chapter 6 and Chapter 7. On the basis of the results the following conclusions were drawn. In the matter of satisfying the export demand, it is seen that in only 3 nos of link canal, viz., Link Canal 1, 5 and 9, the export demands at the exporting points are fully met, whereas in case of Link Canal 8, the achievement is 94.59%. In respect of other Link Canals, the demands met are 6.7% for Link Canal No 2& 3; 41.53% for Link Canal 4; 16.9% for Link Canal No 6; 25.69% for Link Canal 7. Further basinwise, Mahanadi, Krishna and Cauvery fully met the demands where as Godavari fell short of it.